The present invention relates generally to electronic circuits. More particularly, the present invention relates to digital frequency counters that measure the frequency of clock signals.
A discrete digital counter device can be configured as a frequency counter to determine the number of signal cycles per unit of time, or as an interval timer to determine the duration of a signal event. A number of functional forms and applications for counters currently exist, including complex laboratory test instruments, solid state frequency counters, and discrete chip-based interval timers. Chip-based implementations may include sub-function support of application-specific internal frequency or time interval measurements.
As is most often the case, the important clock characteristic of frequency accuracy is left to external measurement hardware located within the system (e.g., a communication system) that utilizes the clock signals. Conventional techniques for monitoring a plurality of clock signals require a plurality of discrete counter devices. In practice, the deployment of a plurality of counter devices may also require a number of interconnecting circuit boards, input and output connections, and other technical considerations that add to the complexity of the application. Such limitations are exacerbated in applications that utilize a large number of clock signals (or other cyclical signals) that may need to be monitored or measured. Another practical limitation of discrete counter devices is that they cannot be utilized to measure the frequencies of internal clock signals, i.e., clock signals that are not accessible via normal output pins of the integrated circuit device.
An embedded counter device according to the present invention can be realized in conjunction with application-specific circuitry to measure any number of internal and/or external clock signals utilized by the application-specific circuitry. The embedded counter device can be implemented in a manner that enables the selective measurement of a number of possible clock signals (the set of measurable unknowns) relative to any one of a plurality of reference signals inclusive of the set of measurable unknowns and exclusive of the unknown itself.
The above and other aspects of the present invention may be carried out in one form by an integrated circuit device having a die, application-specific circuitry formed on the die, where the application-specific circuitry utilizes a number of internal clock signals, and a counter formed on the die. The counter is configured to receive a number of input signals comprising those associated with internal clock signals and those selected from a set of externally applied clock signals.